How hard was it for you to swap those zx6 forks? Are you still using the NSR wheel? ....And how does it feel? Did you have respring it n stuff? Need to find a front end and rvf/rs stuff is getting hard as hell to find.
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MC21 300R w/SE bits, Rossi 2001
MC28SE Silhouette Repsol

It was pretty easy. I pressed out the nsr stem( very easy and I think the best way to do it is on a lathe, by turning off the weld, then using the centre to puch it out with a bit of bar!), then had some custom yokes made up. They weren't massively expensive, and allowed me to keep the nsr geometry correct. The trick is to keep the fork offest at 35mm. The ZX yokes are 20mm... That would make the bike steer like a pissed up crack whore... Or maybe a chopper.

Anyway, once that's done, you can just bolt on the front end as normal. I used a ZX wheel so I'm using a 120 front, but I have a 5.25" rear wheel too, with a 165 rear, so it's effctively 250GP tyre sizes. I primarily chose the ZX front end because of the tiny disks, which keep with the 250 style and are massively powerful anyway. I'd have preferred to stick with a CBR-RR front end if I could, but the disks are huge and pointless.

I haven't changed the geometry at all, so it handles as a goo one should, and I'm quite heavy at a 100Kg, so I haven't changed the internals and it feels great for me. I like it quite firm at the front anyway and it's just that but still supple. Allows you to brake like a biatch too.
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NSR300R - Why did i ever have a 250...

maxim wrote: The trick is to keep the fork offest at 35mm. The ZX yokes are 20mm... That would make the bike steer like a pissed up crack whore...

Can somebody explain this offset clamp thing to me. Where is it measured from and what is the point. Is this a way to change the trail and leave the rake stock? I have 22mm offset clamps on my CRF but I have no idea what that means. We have also been discussing this ont he Ducati forum but nobody has really shed any good information on the subject. Pictures?
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james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

The off set is the distance between the center of the steering stem and the center of the fork legs.

A larger off set of course increases the wheel base where a smaller one shortens it. The smaller the off set the faster the bike will turn. This can also be adjusted by the rake of the forks but this means using off set yoke and stems.

The steeper the rake the faster the bike will turn. This is what happens when you lower the forks though the yokes, you are making the rake steeper.
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If I have to take the carbs off once more...

Thanks Steve, that helps. The guys on the ducati forum were saying to put on 24mm offset forks to 23.5 rake setting, which is is already pretty steep. That would be friggin nuts! How much is too much?
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james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

Tricky subject this one.

A smaller offset increases the trail, which essentially makes the bike more stable (reluctant to turn). The wheel base is also shortened, but because of the increased trail the effect is small.

Increase the offset and the trail is reduced, which make the front feel lighter and easier to turn. The wheel base is increased, but again, the effect is small.

A stock NSR has a trail of 87mm according to the spec, but my measurements say around 84mm, but it's a non stock tyre. this is measured at 23.25 degree steering angle. If you go from 35mm offset to 25mm offset with no other change then the trail increases to about 95mm. Then tip the steering back to 22.5 degrees (RS250 NF5) and you bring the trail back to 90mm. This gives stability and sharp steering. Go to 22.5 degrees with 35mm offset and you'll have 80mm trail which could make the steering a little flighty in the fast bits.

In answer to j911. If you go to 23.5 degrees (more raked out than stock NSR) with 24mm offset (97mm trail) you'll quite frankly have a bike that steers like the old boiler GSXR1100! And I had one of those so don't do it.

All these figures are approximate and just an example of how it works. If you try anything and you crasdh and burn then don't blame me.

Blame Andy. It's his website

That for the reply Matt, but I may now be more confused. I think I may not understand trail correctly.

I found this in an advertisement. Keep in mind that the higher end Ducs have two settings for rake (23.5 & 24.5). I have not fond out what the stock offset is?


Performance billet triple clamp set for the 749/999 series. These have a 27mm offset for better stability and include an aluminum headstock pin and hardware. Available in Silver only with 53/56mm diameter for Ohlins forks. They are also available for Showa forks. No adapter is rquired.

Adjusted in the fast steering head angle (23.5), you will run the same trail as a stock bike which equals superfast turn in, lighter turn in, more feedback from the front tire and more stability out of the chassis. This will allow you adjust to run the rear end of the bike lower for increased traction.

Your forks will sit “lower” in the clamps (higher front end) so in effect the bars get raised 10mm from stock. This is easier on your arms and hands. It is much better for long trips with all the benefits of a perfectly setup bike.

How would changing the offset of only one t-clamp effect the big picture (like many choppers).
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james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

Stephen that's not an ideal way to look at it and as Matt say the wheelbase increase or decreas has limited effect on how the bike steers. If you added 200mm to the wheelbase then you'd be correct but not with figures you get from adjusting the offset. You can get bigger changes from adjusting the chain...

I have a load of data I can dig out and some diagrams I used to calculate the geometry using various tyres if you're interested. My bike keeps the NSR's 35mm offset, 710mm fork length, measured from wheel spindle to top yoke face, and 87mm trail, resulting in the correct rake also when used with a 208GP front...

Changing the offset generally has the biggest effect on steering input and how quickly the bike turns. A reduced 20mm offset would 'increase' the NSR's trail by a substantial amount, from memory to around 104mm. The rake wouldn't necessarily steepen or relax and so you would have a far slower turning bike.

I spoke to these guys when designing the yokes and they have some incredibly useful info on their site and books on chassis design.

http://www.tonyfoale.com/
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NSR300R - Why did i ever have a 250...

As you say maxim it isnt an ideal way to look at it but its simple. Of course you alter the wheel base more by adjusting the chain but not many people think of that. Look in a CR (Honda manual) and there is a page on where to have your wheel adjusted for what condtions! lol
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If I have to take the carbs off once more...